In the prior art there are many types of printers that are used with data processing equipment. Examples of such prior art printers are impact printers which include daisy wheel and dot matrix printers, and laser printers which use a copier process coupled with a laser that writes the material to be printed to an image drum within the printer. There are also many other types of prior art printers. All these prior art data processing printers only do one sided printing, and to accomplish two sided printing, paper already printed on one side must be placed back into the printer to have the reverse side printed. This is an awkward, time consuming process, and mistakes are often made in the process. Attempts to create two-sided printers have resulted in printers having complex paper handling apparatus that print first on one side of the paper and afterwards print on the other side of the paper. Such two-sided printers are expensive and require frequent maintenance, usually by a skilled technician, due to their complicated construction. In addition, one-sided and two-sided printers are separate products and a user of a single-sided printer cannot easily upgrade their one-sided printer to a two-sided printer. Customers must therefore obtain a separate two-sided printer. This usually leaves customers with two printers when all they need is one printer.
Accordingly, there is a need in the art for a printer that can easily and quickly be changed from a one-sided printer to a two-sided printer. In addition, there is a need for a printer that has a relatively simple paper handling mechanism that is used for both one-sided and two-sided printing. There is also a need for a printer that can perform two-sided printing without having to reload paper already printed on one side back into the printer, and that can perform two-sided printing at a much faster rate than heretofore possible. There is also a need in the art for a modular printer having two modular printer mechanisms that can quickly and easily be mounted in or removed from the printer to provide single or double sided printing, for ease of cleaning, other maintenance, and replacement of the printing mechanisms, and that can still provide one-sided printing when one of the two printer mechanisms is disabled.